Es 6 expressions

[Erica42]

Associated Issue: #1884

Summary of Changes

• Changed to import and added exports to functions
• fixed issue with yarn flow

Test Plan

Tell us a little a bit about how you tested your patch.

Example test plan:

• Command-P opens the panel
• Clicking “+” opens the panel
• Clicking a source navigates to the source
• Clicking "x" closes the panel

Here's the Debugger's Testing doc
https://docs.google.com/document/d/1oBMRxV8A2ag2t22YsQOxTdEv0mXKzIg0tggJjRkU1S0/edit#.
Feel free to improve it!

Screenshots/Videos (OPTIONAL)

[codecov]

Codecov Report

Merging #2482 into master will decrease coverage by 0.15%.
The diff coverage is 66.66%.

@@            Coverage Diff            @@
##           master   #2482      +/-   ##
=========================================
- Coverage   54.45%   54.3%   -0.16%     
=========================================
  Files          52      52              
  Lines        2009    2011       +2     
  Branches      392     391       -1     
=========================================
- Hits         1094    1092       -2     
- Misses        915     919       +4

Impacted Files	Coverage Δ
src/reducers/event-listeners.js	22.22% <50%> (ø)	⬆️
src/reducers/expressions.js	20.93% <75%> (-6.73%)	⬇️
src/utils/editor/index.js	11.11% <0%> (-0.76%)	⬇️
src/utils/pause.js	17.64% <0%> (+10.98%)	⬆️

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